1. Field of the Invention
The present invention relates to a process for the dyeing of polymers of ethylene and especially to the dyeing of blends of polyethylene with polymers containing carboxylic acid and certain other polar groups.
2. Description of the Prior Art
Polymers of alpha-olefins in which the alpha-olefin is a hydrocarbon are well known. Such polymers, which include homopolymers of ethylene and copolymers of ethylene with C.sub.3 -C.sub.10 alpha-olefins, are used in large volumes for a variety of end-uses e.g. in the form of fibres, films, moulded articles and the like. If fabricated articles are desired in a colour other than the natural colour of the polymer, it is often possible to pigment the polymer or, especially if the surface of the polymer has been suitably treated, to print the fabricated article. The use of pigments and/or printing techniques depends to some extent on the nature of the fabricated article and the process used in the manufacture of the article.
In some instances, it is desirable or even necessary to be able to dye the fabricated article. In general, hydrocarbon polyolefins are not receptive to dyes, although techniques to render polyolefins receptive to dyes are known, including copolymerization of polar monomers into the polymer. However, polar monomers tend to act as catalyst poisons in ethylene polymerization processes, especially so-called solution polymerization processes, and hence cause process problems or cannot be tolerated in the polymerization process. For some end-uses, the techniques used to render polyolefins receptive to dyes may not be economically attractive and/or may affect deleteriously the properties of the polymer.
The blending of polar polymers with hydrocarbon polyolefins is known. For instance, blends of polyethylene with ethylene/methacrylic acid copolymers that yield films with a high degree of toughness and a high yield strength are disclosed in U.S. Pat. No. 3,709,957 of D. L. Brebner, which issued Jan. 9, 1973. Blends of polyethylene and ionomer polymers intended for the manufacture of film having excellent linear tear properties are disclosed in U.S. Pat. No. 4,098,406 of N. J. Otten et al., which issued July 4, 1978. Ionomer polymers are disclosed in U.S. Pat. No. 3,264,272 of R. W. Rees, which issued Aug. 2, 1966. The dyeing of ethylene polymers blended with copolymers of C.sub.14 or higher alpha-olefins and maleic anhydride is described in U.S. Pat. No. 4,320,046 of R. H. Havens, which issued Mar. 16, 1982.
The dyeing of acrylic polymers with basic dyes is known and is, for instance, described in a manual from Sandoz Ltd. of Basle, Switzerland, entitled "Sandocryl.RTM. B Dyestuffs and Chemicals for the Dyeing and Finishing of Acrylic Fibres". Normally, dyeing is carried out at pH 4.5.